22-05-2025
- Science
- The Herald Scotland
The best way to make a huge splash in the pool (it's very hard to do)
Now, scientists at the Georgia Institute of Technology have worked out the mechanics of exactly what these divers are doing to create their massive splashes - and it's a far cry from the simplicity of a belly buster.
"It's very difficult to master, it can be quite dangerous, and it requires millisecond control," said Pankaj Rohilla, a postdoctoral researcher and co-author on the paper "Mastering the Manu--how humans create large splashes," published on May 19.
The Georgia Tech team of fluid dynamics and biomechanics experts spent months working on the problem.
Learning the mechanics involved analyzing more than 75 videos of people doing manu jumps, then taking lab members to Georgia Tech's pool to do more than 50 trial jumps, all filmed in high definition to capture exactly what their bodies were doing at each millisecond.
Finally, researcher and co-author Daehyun Choi built a "Manubot," a hand-sized robot that could mimic a diver's body movements during a manu jump to test what exact angle was best to create the biggest possible movement of water.
Making the biggest splash possible
What Maori jumpers have perfected turns out to involve specific movements all done within as little as 0.14 seconds of each other -- and the exact opposite of the techniques taught to traditional divers, as seen every four years during the Olympics.
"It's all about making a V-shape with your body during water entry and then a specific set of underwater body dynamics," said Rohilla.
Specifically, the best manu jumpers form a perfect 45-degree V with their bodies in the air. Then, as soon as they touch the water's surface, the diver rolls back and kicks to straighten their body out.
This expands the air cavity created when their body enters the water. The height of the splash corresponds to the size of that cavity. The time of cavity collapse is known as the "pinch-off time." Gravitational forces push the water back in the vertical direction, generating an upward jet of water.
"It's basically about how much energy you're trapping underwater," said Rohilla.
Technically, the initial splash created by the diver's body entering the water is called the crown splash, while the second, caused by the collapsing air cavity, is called a Worthington jet.
It requires extreme body control and split-second timing. The V-shape of the body has to be a 45-degree angle to create the fastest and highest Worthington jet, while ensuring the diver's safety.
The roll back and kick motion must occur within 0.14 to 0.15 seconds of entering the water when the diver is jumping from 3 meters, said Rohilla. That's about 10 feet high.
The higher the jump, the shorter the time the diver has to perform the roll back and kick.
"It looks easy but it's actually very challenging," he said.
Manu diving can hurt
The researchers caution that the manu maneuver is not only difficult but can be risky and painful.
"The higher you jump, the less reaction time you have. So it can be quite dangerous," said Rohilla.
Especially if you miss the landing shape of 45 degrees, the water can slap the diver's back with a lot of force.
"That hurt a few of our teammates. It was very painful," Rohilla said. "You could even hurt your spine, so it can be a risky sport."
Manu diving has been banned in some pools in New Zealand, including one area where a child was injured.
A Maori cultural sport
The sport back at least several decades and has become an important cultural tradition in New Zealand.
The name most likely comes from the Maori word "manu" which means bird, though some suggest it's a shortened form of Mangere, a suburb of Auckland where the sport is popular.
It's gone from something people did for fun to showing off their prowess as a competitive sport. In 2024, the first Manu World Championships were held in New Zealand's capital, Wellington. Other competitions appeared to have been held dating back to at least 2011.
In Wellington this year, more than $23,000 in prize money is on the line. Jump heights range from three feet above the water for children to as high as 16 feet for adults.
Divers can compete in the traditional manu style of the V-Bomb, but new styles have also been introduced, including The Gorilla, the Cannonball, and The Coffin.
The competition uses high-tech cameras to calculate the splash height of each diver to ensure fair scoring.
'Thousands and thousands of hours of practice'
The fun of manu diving is making a huge splash, something people love given the quantity of splashes observed wherever children play in pools.
It's also the exact opposite of the clean, minimal splash demanded in competitive diving, where scoring depends, in part, on producing the smallest possible splash as the diver plunges into the water.
"We call it 'ripping,'" said Phil Tonne, a dive coach at the University of California, Davis. "The least amount of splash correlates to the highest scores."
Making no splash is as hard as making a big splash. "You want to be as streamlined as you can possibly get," Tonne said. "It takes thousands and thousands of hours of practice."
